Balefang the Unslayable is a rare Legendary Creature — Demon Dragon card from Mystery Booster: Commander Edition (MBC), collector number 20.
Flying, trample, protection from Angels and from Archons Players can't gain life. When Balefang enters, target opponent creates a tapped Baneslayer Angel token. The token is goaded for the rest of the game. (It's a {3}{W}{W} 5/5 Angel creature with flying, first strike, lifelink, and protection from Demons and from Dragons.)